Conventionally, power supply apparatuses (power supply circuits) for converting alternating current power to direct current power using a rectifier circuit have been known. In a power supply apparatus of this type, a high frequency current tends to be generated, resulting in reduction in power supply efficiency. To prevent such reduction in power supply efficiency, for example, Patent Document 1 discloses a power supply apparatus configured to reduce the high frequency current using a so-called PAM (pulse amplitude modulation) control.
Specifically, the power supply apparatus of Patent Document 1 includes a rectifier circuit, which is a diode bridge circuit, and a smoothing circuit. The smoothing circuit includes two capacitors coupled in series with each other, and a single capacitor coupled in parallel with the two capacitors and is configured to perform double voltage rectification between the smoothing circuit and the rectifier circuit. The power supply apparatus further includes a switching element, provided at an output terminal of the rectifier circuit, for causing, when being turned ON, a short-circuit for output power of the rectifier circuit.
In the power supply apparatus, PAM control is performed. Specifically, in the rectifier circuit, the switching element is switched according to zero-cross points of an input voltage so that a waveform of an input current approximates to a waveform (a sine wave) of an input voltage. That is, an ON duty of a PAM waveform is controlled by this switching operation, so that the waveform of an input current approximates to a sine wave. Accordingly, the high frequency current is reduced.    Patent Reference 1: Japanese Published Application No. 2001-145358